This application claims the priority of Korean Patent Application Nos. 2003-58790, filed on Aug. 25, 2003, and 2004-2925, filed on Jan. 15, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a recording medium, a memory device including the recording medium, and methods of writing and reading data for the memory device, and more particularly, to a recording medium including a ferroelectric layer, a nonvolatile memory device including the recording medium, and methods of writing and reading data for the nonvolatile memory device.
2. Description of the Related Art
As the demand for small and thin electronic devices such as mobile telecommunication devices and electronic notes increases, the necessity of ultra-small and integrated memory devices also increases. However, there are limitations in minimizing the size of a hard disk which is a conventional data storage device. A flash memory could be used as an alternative to the hard disc, however, it is very difficult to enhance integration degree of the flash memory. Therefore, a new, ultra-small, highly-integrated, nonvolatile memory device is required. For this purpose, a memory device using a scanning probe (hereinafter probe) has been developed.
For an ultra-small and integrated memory device that uses the probe when reading data, a ferroelectric layer, a ferromagnetic layer, a thermoplastic resin, and a thermosetting resin have been developed as alternative recording media.
Data recorded in the alternative recording media can be read by applying a sensing force to the probe such as an electrostatic force, a static magnetism force, piezoelectric force, etc., and sensing changes in electrical characteristics of the recording medium, for example, differences in electrical and thermal conductivity.
A memory device that senses a polarized state of a domain of the ferroelectric layer using piezoelectric force utilizes a lock-in amplifier, and thus, it is difficult to sufficiently reduce the size of the memory device.
Data can be written in the recording medium by inverting the domain of the ferroelectric layer or the ferromagnetic layer with the probe, or by heating the recording medium to produce a phase transition or damage an area where data will be recorded. The latter method, that is, the heating method, proceeds very slowly and is disadvantageous when the reading and writing processes are repeated.
Ultra-small and integrated memory devices have been developed by combining the aforementioned methods. These memory devices are categorized into two types depending on whether the probe contacts the recording medium.
If the probe does not contact the recording medium, while data is read, an extra feed back circuit is required to maintain a constant distance between the probe and the recording medium. Thus, it is difficult to minimize the size of the memory device for mobile products.
On the other hand, if the probe contacts the recording medium, while data is read, abrasion of the probe and-the recording medium, especially that of the recording medium, may be a serious problem. In addition, data reading speed can be limited due to the resonance frequency of a cantilever (normally 1 MHz or less) which supports the probe.